The more I think about it, the more I think it should be NOT a pop-up but the game pausing and pulling up a UI panel with all your available Reactions only
Those are literally the same thing. It's exactly how it works in Solasta and how everyone is calling it.
No. It's not.
Solasta be like: Big window telling me "Enemy is going to run away from you and you can do an attack of opportunity. Would you like to do an attack of opportunity?"
Lots of words. Big window.
I was saying something more like as the enemy is trying to run away, the game pauses and the UI flashes, showing your melee button. This lets you know that you can attack as a reaction. No words except maybe in the combat log if you open it. Also, first time it happens, tooltips tell you it means you can do a reaction.
Similar mechanics. Different presentation.
I don't know. I'm still trying to figure out a more fast paced Reactions system with Scripted Reactions. Most of the reactions in 5e really could be managed fairly well with Scripted Reactions. This would minimize the number of Reactions that would actually cause the game to pause
